CARACTERISTATION ET ETUDE DE LA FONCTION DE LA PROTEINE KINASE RSK2 IMPLIQUEE DANS LE SYNDROME DE COFFIN-LOWRY

LE SYNDROME DE COFFIN-LOWRY (CLS) EST UNE MALADIE HEREDITAIRE RARE LIEE AU CHROMOSOME X QUI ASSOCIE UN RETARD MENTAL PROFOND A DES ANOMALIES SQUELETTIQUES SEVERES. DES ETUDES DE LIAISON ONT PERMIS, EN 1992, DE LOCALISER LE GENE CLS EN XP22. J'AI PARTICIPE EN 1996 A L'IDENTIFICATION DU GENE RSK2 RESPONSABLE DE LA MALADIE. LES PROTEINES RSK (RIBOSOMAL S6 KINASE) FORMENT UNE FAMILLE DE SERINE/THREONINE KINASES INTERVENANT DANS LA VOIE DE TRANSDUCTION DU SIGNAL RAS/MAPK ACTIVEE PAR DES AGENTS MITOGENES. LA CARACTERISTIQUE PRINCIPALE DES RSKS, COMMUNE AUX MSKS (MITOGEN-AND STRESS-ACTIVATED PROTEIN KINASE), EST D'AVOIR DEUX DOMAINES DE KINATION ACTIFS NON HOMOLOGUES. J'AI CARACTERISE LA STRUCTURE DU GENE CE QUI M'A PERMIS DE DEFINIR DES AMORCES INTRONIQUES AFIN DE TESTER LES 22 EXONS COMPOSANT LE GENE PAR LA TECHNIQUE DE SSCP. UNE RECHERCHE SYSTEMATIQUE DE MUTATIONS CHEZ PLUS DE 200 PATIENTS A MIS EN EVIDENCE UNE TRES GRANDE HETEROGENEITE DE MUTATIONS CONDUISANT, POUR LA PLUPART, A LA PERTE DE FONCTION DE LA PROTEINE. CHEZ UN PATIENT EXPRIMANT UNIQUEMENT UN RETARD MENTAL LEGER SANS AUTRE SIGNE CLINIQUE (MRX), J'AI IDENTIFIE UNE MUTATION PRODUISANT UNE PROTEINE AYANT UNE ACTIVITE RESIDUELLE DE 20%. AFIN DE DETERMINER LE ROLE PHYSIOLOGIQUE DE LA PROTEINE RSK2 AU COURS DU DEVELOPPEMENT, DANS LA DIFFERENCIATION ET LA CROISSANCE CELLULAIRE, NOTAMMENT AU NIVEAU DU SQUELETTE ET DU SYSTEME NERVEUX, J'AI ENTREPRIS LA CONSTRUCTION D'UN MODELE MURIN PAR INACTIVATION DU GENE RSK2 PAR RECOMBINAISON HOMOLOGUE. DEUX MODELES ONT ETE OBTENUS : L'UN EXPRIMANT PROBABLEMENT UN FAIBLE TAUX DE PROTEINE RSK2 (RSK2 H) ET L'AUTRE NE L'EXPRIMANT PLUS DU TOUT (RSK2 ). LES SOURIS RSK2 H ET RSK2 SONT VIABLES ET NE PRESENTENT PAS D'ANOMALIES MORPHOLOGIQUES EVIDENTES. J'AI ANALYSE LES ANIMAUX RSK2 H DANS LE CADRE D'ETUDES COMPORTEMENTALES. DES TESTS DE LOCOMOTION AINSI QUE DIFFERENTS TESTS COGNITIFS, NOUS ONT PERMIS D'IDENTIFIER UN DEFICIT D'APPRENTISSAGE ET DE MEMOIRE SPATIALE. NOUS AVONS ENTREPRIS DES ETUDES FONCTIONNELLES DE LA PROTEINE RSK2. NOUS AVONS PU IDENTIFIER, EN ETUDIANT DES FIBROBLASTES DE PATIENTS AINSI QUE LES CELLULES SOUCHES EMBRYONNAIRES RSK2 H, DEUX SUBSTRATS SPECIFIQUES DE RSK2 : LE FACTEUR DE TRANSCRIPTION CREB ET L'HISTONE H3.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

P90 Ribosomal s6 kinase 2 negatively regulates axon growth in motoneurons.

International audienceMutations in Ribosomal s6 kinase 2 (Rsk2) are associated with severe neuronal dysfunction in Coffin-Lowry syndrome (CLS) patients, flies and mice. So far, the mechanisms of how Rsk2 regulates development, maintenance and activity of neurons are not understood. We have investigated the consequences of Rsk2 deficiency in mouse spinal motoneurons. Survival of isolated Rsk2 deficient motoneurons is not reduced, but these cells grow significantly longer neurites. Conversely, overexpression of a constitutively active form of Rsk2 leads to reduced axon growth. Increased axon growth in Rsk2 deficient neurons was accompanied by higher Erk 1/2 phosphorylation, and the knockout phenotype could be rescued by pharmacological inhibition of MAPK/Erk kinase (Mek). These data indicate that Rsk2 negatively regulates axon elongation via the MAPK pathway. Thus, the functional defects observed in the nervous system of CLS patients and animal models with Rsk2 deficiency might be caused by dysregulated neurite growth rather than primary neurodegeneration

Unreported RSK2 missense mutation in two male sibs with an unusually mild form of Coffin-Lowry syndrome

International audienceAn unreported missense mutation of the ribosomal S6 kinase 2 (RSK2) gene has been identified in two male sibs with a mild form of Coffin-Lowry syndrome (CLS) inherited from their healthy mother. They exhibit transient severe hypotonia, macrocephaly, delay in closure of the fontanelles, normal gait, and mild mental retardation, associated in the first sib with transient autistic behaviour. Some dysmorphic features of CLS (in particular forearm fullness and tapering fingers) and many atypical findings (some of which were reminiscent of FG syndrome) were observed as well. The moderate phenotypic expression of this mutation extends the CLS phenotype to include less severe mental retardation and minor, hitherto unreported signs. The missense mutation identified may be less deleterious than those previously described. As this mutation occurs in a protein domain with no predicted function, it could be responsible for a conformational change affecting the protein catalytic function, since a non-polar amino acid is replaced by a charged residue

J Neurosci

More than 80 human X-linked genes have been associated with mental retardation and deficits in learning and memory. However, most of the identified mutations induce limited morphological alterations in brain organization and the molecular bases underlying neuronal clinical features remain elusive. We show here that neurons cultured from mice lacking ribosomal S6 kinase 2 (Rsk2), a model for the Coffin-Lowry syndrome (CLS), exhibit a significant delay in growth in a similar way to that shown by neurons cultured from phospholipase D1 (Pld1) knock-out mice. We found that gene silencing of Pld1 or Rsk2 as well as acute pharmacological inhibition of PLD1 or RSK2 in PC12 cells strongly impaired neuronal growth factor (NGF)-induced neurite outgrowth. Expression of a phosphomimetic PLD1 mutant rescued the inhibition of neurite outgrowth in PC12 cells silenced for RSK2, revealing that PLD1 is a major target for RSK2 in neurite formation. NGF-triggered RSK2-dependent phosphorylation of PLD1 led to its activation and the synthesis of phosphatidic acid at sites of neurite growth. Additionally, total internal reflection fluorescence microscopy experiments revealed that RSK2 and PLD1 positively control fusion of tetanus neurotoxin insensitive vesicle-associated membrane protein (TiVAMP)/VAMP-7 vesicles at sites of neurite outgrowth. We propose that the loss of function mutations in RSK2 that leads to CLS and neuronal deficits are related to defects in neuronal growth due to impaired RSK2-dependent PLD1 activity resulting in a reduced vesicle fusion rate and membrane supply

Long-term outcome after infliximab for refractory ulcerative colitis

Background and aims: Infliximab (IFX) has been shown efficacious for moderate-to-severe ulcerative colitis (UC), but data on long-term efficacy are tacking. We investigated long-term outcome including colectomy rates in outpatients treated with IFX for refractory UC in a single referral centre, and evaluated if predictors could be identified. Methods: The first 121 outpatients (median age 38.0 years) with refractory UC treated with IFX were included. The primary outcome was colectomy-free survival. Secondary measures were sustained clinical response and serious adverse events. Results: From the 81 patients (67%) with an initial clinical response to IFX, 68% had a sustained clinical response. No independent predictors of sustained clinical response could be identified. Over a median (IQR) follow-up period of 33.0 (17.0-49.8) months, 21 patients (17%) came to colectomy. Independent predictors of colectomy were absence of short-term clinical response [Hazard ratio 10.8 (95% Cl 3.5-32.8), p = 5 mg/L [Hazard ratio 14.5 (95% Cl 2.0-108.6), p=0.006] and previous IV treatment with corticosteroids and/or cyctosporine [Hazard ratio 2.4 (95% Cl 1.1-5.9), p=0.033]. Six patients developed a serious infection, three a malignancy, two a post-operative complication and one patient died (suicide). Conclusions: With a median follow-upof 33.0 months after start of IFX, 17% of patients with refractory UC needed colectomy, while sustained clinical response was present in 68% of initial responders. (c) 2008 European Crohn's and Colitis Organisation. Published by Elsevier B.V. All rights reserved

Anchored p90 Ribosomal S6 Kinase 3 Is Required for Cardiac Myocyte Hypertrophy

RATIONALE: Cardiac myocyte hypertrophy is the main compensatory response to chronic stress on the heart. p90 Ribosomal S6 Kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. Although increased RSK activity has been observed in stressed myocytes, the functions of individual RSK family members have remained poorly defined, despite being potential therapeutic targets for cardiac disease. OBJECTIVE: To demonstrate that type 3 RSK (RSK3) is required for cardiac myocyte hypertrophy. METHODS AND RESULTS: RSK3 contains a unique N-terminal domain that is not conserved in other RSK family members. We show that this domain mediates the regulated binding of RSK3 to the muscle A-kinase anchoring protein (mAKAP) scaffold, defining a novel kinase anchoring event. Disruption of both RSK3 expression using RNA interference and RSK3 anchoring using a competing mAKAP peptide inhibited the hypertrophy of cultured myocytes. In vivo, RSK3 gene deletion in the mouse attenuated the concentric myocyte hypertrophy induced by pressure overload and catecholamine infusion. CONCLUSIONS: Taken together, these data demonstrate that anchored RSK3 transduces signals that modulate pathologic myocyte growth. Targeting of signaling complexes that contain select kinase isoforms should provide an approach for the specific inhibition of cardiac myocyte hypertrophy and for the development of novel strategies for the prevention and treatment of heart failure

Surgical Emergencies in Crohn’s Disease

Crohn’s disease, as a chronic inflammatory disease of unknown etiology that can affect any part of the alimentary canal from the mouth to the anus, has a highly variable course and a very unpredictable evolution. Even surgery does not cure CD, it has however a relevant role in its treatment in combination to medical therapy during the large course of the disease; indeed almost each patient is submitted to a surgical intervention during his life. Nowadays, surgery is considered the last treatment to use whenever medical therapy is insufficient to control symptoms; this choice involves an intervention on more serious patients with more surgical complications. Surgery finds in the Crohn’s disease a main role in the management of the obstructive or septic complications; however, elective surgical treatments are proposed in patients with sub-occlusive presentation due to chronic fistulas or with high CD index (>220) with a terminal ileum-cecum disease